WO2000016359A2 - System of absolute measurement for radiological image luminance control - Google Patents
System of absolute measurement for radiological image luminance control Download PDFInfo
- Publication number
- WO2000016359A2 WO2000016359A2 PCT/US1999/020729 US9920729W WO0016359A2 WO 2000016359 A2 WO2000016359 A2 WO 2000016359A2 US 9920729 W US9920729 W US 9920729W WO 0016359 A2 WO0016359 A2 WO 0016359A2
- Authority
- WO
- WIPO (PCT)
- Prior art keywords
- crt
- luminance
- ambient
- photosensor
- photocell
- Prior art date
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Classifications
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
- H04N5/00—Details of television systems
- H04N5/44—Receiver circuitry for the reception of television signals according to analogue transmission standards
- H04N5/57—Control of contrast or brightness
- H04N5/58—Control of contrast or brightness in dependence upon ambient light
Definitions
- This invention relates to cathode ray tube (“CRT") display of radiographic and other images of critical contrast detail by computer-controlled technique, and more particularly, to an improved system for measuring the absolute luminance of the CRT display and the actual effective luminance as would be measured from the viewer's perspective due to additional reflected ambient illuminance in order to enable closed loop adjustment of the display device and to thereby facilitate image perception and ascertain fidelity of image presentation conveniently over time.
- Such absolute measurements of device luminance performance and viewing environment can be reported to the presenting computer for optimization of task dependent image processing and quality control.
- digital representations of images from various digital modalities are stored in computer memory and on computer media.
- the image representations are retrieved and displayed in any of various locations where there is such a display terminal for presentation, consultation, analysis, interpretation, and/or diagnosis.
- the digital representation of an image is converted to a matrix of quantified (pixel) values which ultimately determine the luminance of a uniquely associated area of the CRT face.
- the image is maintained for multiple seconds.
- the fidelity of image representation is inherently well-controlled by nature of its digital embodiment and conventional digital system practices.
- the perceived image may differ from the "true" image as control for this final step has historically remained far less stringent.
- the ultimate consequences that result from suboptimal control range in significance from lowered productivity to missed pathology.
- the CRT display device may be installed and certified to operate at an established luminance specification. Over time (which may vary from weeks to years depending on usage and design compromises) the effective luminance performance will degrade in response to factors such as "aging" of the cathode, phosphor, and glass (browning). It is desirable to be able to compensate for these inevitable CRT effects automatically.
- the ambient light levels where the CRT display device is being used may be variable. It is not practical to always set room ambient lighting levels to accommodate the CRT display intensity for optimal image perception. The opposite may be desired: One wishes to establish display intensity, within the capability of the display device, as will maximize image fidelity by compensating for ambient lighting levels determined by a more critical task. As a simplified example, in a darkened room where ambient light level is low, minimum display luminance need be selected so that image areas of differing low brightness may be discerned without creating the perception of false contours while areas of higher brightness do not coalesce unnecessarily.
- image areas of differing low luminance may fail to be discerned because of degraded contrast, even when image areas of higher brightness are entirely and accurately readable. It is desirable to present the image for maximum perceived contrast commensurate with the luminance specification of the CRT device and the level of ambient illuminance.
- the X axis represents the constant video drive level presented to the device over a display area and the Y axis represents the luminance value measured at the corresponding display area.
- the video drive level is a voltage between 0 volts (black) and .7 volts (white) or whatever video range is provided by the computer image source; here the video signal level is represented by an 8 bit digital value from 0 to 255.
- the absolute luminance is measured with a calibrated photometer (here in candelas per square meter) and plotted logarithmically to facilitate the comparison with the photopic brightness (perceptual) response of the human visual system to luminance (approximately logarithmic). Note that at drive levels where the graph takes on a more horizontal slope the luminance differences for equal changes in drive become correspondingly difficult to perceive.
- the first effect (display device does not meet luminance specification) can be readily determined from the endpoints of the graph, the maximum and minimum luminance of the display device.
- the solid line graph represents the characteristic curve of the same display device with ambient light included at the face of the CRT such that the resulting component which is reflected from the face (glass and phosphor) of the CRT over the area being measured by the photometer is not negligible.
- a measure of the second effect luminance distortion from ambient light is readily distinguished by comparing the graphs.
- the goal is automatically to determine the luminous response of the monitor and then adjust CRT levels to ensure perception of all displayed pixel level differences (particularly in the "dark" areas) which might otherwise be obscured by ambient light to an accommodated viewer while maintaining an adequate overall contrast ratio of the display device.
- the medical professional looking at the image may be presented with a risk of missing critical details of the image. For example, the slight but clinically significant shading within a radiological image might not even be perceived.
- Technology for the demanding ambient of a cockpit is addressed with multiple sensors in U.S. Patents 5,057,744; and 5,270,818.
- These prior ambient light-sensing arrangements are not believed to be fully suitable for CRT display of radiologic and other static images displayed by computer-controlled technique for critical interpretation because a direct measurement of ambient light level, as by using a photocell exposed through an aperture to the room ambient, as heretofore known, may not adequately sense the true illumination impinging over the CRT face.
- the sensor's independent collector is subject to accumulation of dust which will effect its response and, without appropriate filtering to match the spectral response of the human eye.
- the system may over-respond to infrared or other invisible radiation as is prominent in the spectrum of some artificial lighting.
- Such a constant contrast system is evidenced by Newman in U.S. Patent 3,649,755.
- Such a system must position the logarithmic sensor to receive the identical proportion of image brightness to ambient brightness as would be seen by the viewer who would observe the contrast ratio as invariant.
- Such a position is only certain to be at the same nominal place as the observer's eye and thus is obtrusive.
- the absence of ambient brightness is not an uncommon situation for critical contrast viewing.
- Gain adjustment of such a system is not only a function of the luminance performance of the device "'hardware" and the ambient illuminance but also depends on the image "software” being displayed (a uniformly light gray image will be presented indistinguishably from a uniformly dark gray image).
- Such an "editorializing" system may not be compatible for the presentation of processed digital images which have already undergone optimization.
- the invention is specifically concerned with the luminance performance of a CRT display device within its ambient environment; the invention does not address other critical characteristics of display device fidelity such as spatial resolution or modulation transfer function.
- the invention presumes no specific knowledge of the task of the viewer or what the image represents hence no form of image dependent processing or adjustment is effected. Rather, the invention enables predictable and expedited image perception over time and location for a class of equipment which would otherwise require ongoing intervention by operator or maintenance personnel to ascertain luminance quality control. Only with such luminance quality control can task or image dependent processing be expected to consistently achieve an advantageous or even reproducible visual change across multiple displays.
- a system for measuring the absolute luminance of a CRT display device and the absolute luminance as would be measured from a viewer's perspective due to the additional reflected contribution of the ambient illuminance such measurements being utilized in a closed loop to effect the necessary adjustments which determine in combination the absolute levels of maximum and minimum luminance of the CRT display device in response to monitored variations in equipment performance and in ambient lighting, such measurements also being available through standard video cabling to the host computer
- the system comprising in combination an image display device including a CRT for computerized display of radiological images, the perception of which varies with luminance presentation and ambient illuminance
- the system further comprising a photosensor unobtrusively carried in relation to the CRT such that light generated internally by the CRT phosphor will be received by the photocell and in the absence of such light that resulting from the ambient lighting at the face of the CRT will predominate at the photocell, circuitry and processing algorithms to interpret the output of the photocell and to enable complete blanking of the CRT phosphor.
- the inventive system effectively measures and facilitates compensation for variations in luminance performance and ambient light which otherwise tend to interfere with the fidelity or facility of image interpretation of computerized static images, especially radiological images, displayed by the CRT.
- FIG. 1 is an illustrative "characteristic curve" for a monochrome CRT display __ device. Measured luminance is plotted for the standard range of video input signal (black to white). The lower (dashed) curve represents a measure of luminance from the phosphor exclusively (no ambient lighting). The upper (solid) curve represents a measure of the luminance from the CRT face which includes both the phosphor contribution and the reflected component from typical ambient room lighting as observed from the perspective of a viewer of the CRT face.
- FIG. 2 is partial cutaway section of a CRT (Cathode Ray Tube), showing only certain portions to one side of a horizontal centerline through the electron gun assembly.
- the figure is otherwise greatly simplified, conceptually illustrative of only salient aspects of the system which are required of or proximate to the physical CRT, and includes circuit features in block diagram form.
- FIG. 3 is a block diagram illustrative of the signals which may be sensed and generated by the system as embodied within a classical CRT display device.
- the inventive system enables automatic and unobtrusive measurement of absolute CRT display luminance and the actual effective luminance as would be measured from the viewer's perspective due to additional reflected ambient illuminance in order to enable closed loop adjustment of the display device with features evident from the following description.
- a photosensor namely a photocell 24, is specially affixed to the exterior surface of the conventional glass envelope, "jug", 35 of the CRT in such a manner and location that: 1) the sensor is not visible to a viewer of the face of the CRT; 2) the sensor and CRT are intimately sealed so that their optical coupling cannot be affected over time by dust, oil, or other airborne contaminants; 3) the sensor "sees” a combination of light from two principal sources, excited CRT phosphor and ambient illumination on the face of the CRT.
- a spectral filter 28 in the form of a thin translucent layer with spectral properties such that the product of the wavelength response of the photocell and that of the translucent layer match the spectral sensitivity response of the human eye.
- Spectral matching layer 28 may be integrally formed as a unit with photocell 24 for being affixed to the CRT as a single layer, as by light-transmissive adhesive.
- the photocell is a linear device such that its output signal may be the sum of two components, one which is proportional to the absolute luminance of the excited phosphor as measured at the face of the CRT and the other which is proportional to the ambient illuminance as measured at the CRT face.
- photocell 24, is a silicon photodiode which produces a current directly proportional to the number of photons (light flux) impinging on its active surface per unit time.
- the photodiode sensitivity (active surface area) must be sufficient to produce a useable signal over the complete range of light to be sensed and measured which as a practical minimum is 5 decades with an effective minimum signal level of roughly 1 picoampere.
- the actual minimum signal depends on the optical transmission parameters of the faceplate 30 and jug 35 of the CRT tube. These parameters normally have a wide range so that each photodiode and CRT combination must be calibrated as a unique pair to determine the particular set of independent linear constants for the measure of ambient and phosphor-sourced light.
- the photocell is mounted in any practical location so as to be responsive to two components of light, one which is proportional to the absolute luminance of the excited phosphor as measured at the face of the CRT and the other which is proportional to the ambient illuminance as measured at the CRT face.
- the resulting signal response can be represented:
- L is the instantaneous magnitude of the sensor response
- P is the instantaneous luminance measured at the face of the CRT due to uniform excitation of a defined area of the display phosphor
- A is the ambient illumination at the face of the CRT
- Kl and k2 are the appropriate linear calibration constants for the phosphor and ambient components.
- the photosensor is preferably positioned upon a surface location 25 of envelope 35 rearwardly of not only face 30 but also rearwardly of a _ phosphor layer 33 applied internally of face 30, at position 25 on what may be regarded as a shoulder of the envelope where it 35 takes on a quasiconical or frustoconical configuration and proceeds sloping toward the neck 36 of the tube.
- the CRT envelope 0 u g) conventionally is provided with an external conductive light shield 39 which may be a coating normally occupying the region of the photocell, but for the present purposes including a window 25 opening therethrough in the position of the photocell and associated spectral layer for transmission of light from the envelope to the photocell.
- Interconnected and proximally associated with photocell 24 is circuitry to amplify and transform the sensor output to a binary signal which can be readily interpreted by a microprocessor control.
- a low impedance current to frequency converter transforms the sensitive analog output of the photosensor to a buffered binary signal with a dynamic range of at least 5 decades.
- the microprocessor control interprets the resulting binary signal.
- the phosphor contribution P to' the signal L of equation 1 has a period corresponding to the vertical refresh or frame time of the CRT display device.
- a timing signal 12 (figure 3) at this rate is provided from the display device to the microprocessor control to facilitate computation of the average frequency over precisely an integral number of frame periods. Additionally the control can cause absolute blanking of the CRT which, in the preferred embodiment, can be effected by sufficient reduction of the positive voltage at the G2 element of the CRT electron gun independent of the video signaling level between the cathode and Gl elements.
- photocell 24 effectively "sees” a combination of proportionate light generated from the phosphor layer and ambient illumination at the CRT face; and it will be appreciated that photocell 24 provides a relative illuminance signal for measurement when the phosphor is not stimulated; but when the phosphor is thereafter excited by the electron beam, the resulting relative luminance (CRT phosphor) is discernible as the increase above the relative illuminance (ambient) measurement.
- B so measuring the minimum luminance (the relative luminance value taken with analog video signal at minimum over the entire display, "black”) and maximum luminance (the relative luminance value with analog video signal at maximum over the entire display, "white”), the endpoints of the characteristic curve for the device (figure 1) are determined.
- FL FP + FA
- FP the frequency due to the phosphor generated light at the photocell 24
- FA the frequency due to the ambient-sourced light at the photocell 24.
- FP is then proportional to the absolute luminance measured at the face of the CRT.
- the conversion constant, CP is the slope between pairs of luminance and frequency measurements made with no ambient illumination (phosphor luminance only), using the identical uniform test pattern, and is determined for each set of CRT, photocell, and circuitry (photosensor responsive means). The constant is stored with the set for access by the microprocessor control.
- This calibration constant, CE enables determination of the effective __ characteristic curve (solid graph, figure 1) of the CRT in the presence of the particular level of ambient illuminance through calculations of the microprocessor control.
- the actual luminance adjustment of the CRT display is in turn established by action of the microprocessor control on the effective gain and offset (or contrast and brightness, or in fact any two basis controls which, together, can determine 2 independent operating points in the plane of the characteristic curve, figure 1) of the video driver for the CRT display device.
- the choice of basis controls will depend on the particular design of the CRT monitor (video amplifier) to which the inventive system may be "added " (figure 3).
- the shape of the characteristic curve may be effectively modified by the imposition of a nonlinear lookup table for the digital pixel values of the image before presentation to the display device.
- the maximum achievable contrast cannot be enhanced, merely redistributed.
- absolute luminance measurement and feedback to 2 basis controls of the display device constitutes "feedback control in 2 dimensions" but is fundamentally different from image processing (modification of pixel data with a dependency on their 2 dimensional position within the image) as taught in other art such as by Haendle et al. in US Patent 5,444,755.
- feedback control in 2 dimensions differs from previous art which would effect 'ambient light compensation' in which there is one basis dimensional control for a single sensor and thus cannot simultaneously and independently establish both end points (max and min luminance) of the characteristic curve.
- ___ The luminance settings are established through one or more "closed loops" which may include: 1) feedback to match measured maximum and minimum luminance to factory values as an initialization procedure 2) proportionate increase of maximum luminance and/or decrease of minimum luminance for a measured increase of ambient illumination before a new image is displayed 3) report change in measured illumination and luminance of a displayed image to a remote processor for task dependent interpretation and determination of optimal luminance compensation which is in commanded back to the display device.
- Such reports and commands may be communicated through any I 2 C (Video Electronics Standards Association, DDC), RS232, local peripheral bus or other serial channel of the display device. It is found that the system thus effectively provides absolute luminance and illuminance measurements from a single sensor to effect visual image fidelity over changes in device performance and ambient lighting without user intervention.
- I 2 C Video Electronics Standards Association, DDC
- RS232 Remote RS232
- local peripheral bus or other serial channel of the display device.
- the CRT may be of monochromic type, and for which gray-scale data of desired resolution may be provided
- the present invention may be used in connection with color displays, as in the graphics arts or home theater applications and for which color temperature, balancing and relative luminance, for example, may presuppose a convenient absolute measurement display-control need similar to that which motivates the present invention, which may thus be used to advantage in connection with such color displays.
Abstract
Description
Claims
Priority Applications (3)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
AU61404/99A AU6140499A (en) | 1998-09-15 | 1999-09-10 | System of absolute measurement for radiological image luminance control |
JP2000570803A JP2002525898A (en) | 1998-09-15 | 1999-09-10 | Absolute measurement system for radiological image brightness control |
EP99948174A EP1119982A4 (en) | 1998-09-15 | 1999-09-10 | System of absolute measurement for radiological image luminance control |
Applications Claiming Priority (2)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
US09/153,629 | 1998-09-15 | ||
US09/153,629 US6327708B1 (en) | 1998-09-15 | 1998-09-15 | System of absolute measurement for radiological image luminance control |
Publications (2)
Publication Number | Publication Date |
---|---|
WO2000016359A2 true WO2000016359A2 (en) | 2000-03-23 |
WO2000016359A3 WO2000016359A3 (en) | 2000-07-27 |
Family
ID=22548021
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
PCT/US1999/020729 WO2000016359A2 (en) | 1998-09-15 | 1999-09-10 | System of absolute measurement for radiological image luminance control |
Country Status (5)
Country | Link |
---|---|
US (1) | US6327708B1 (en) |
EP (1) | EP1119982A4 (en) |
JP (1) | JP2002525898A (en) |
AU (1) | AU6140499A (en) |
WO (1) | WO2000016359A2 (en) |
Cited By (1)
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EP2252049A1 (en) * | 2009-05-14 | 2010-11-17 | Marc Leppla | Method for calibrating a monitor and sensor for measuring light intensity |
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US6411306B1 (en) * | 1997-11-14 | 2002-06-25 | Eastman Kodak Company | Automatic luminance and contrast adustment for display device |
US6611297B1 (en) * | 1998-04-13 | 2003-08-26 | Matsushita Electric Industrial Co., Ltd. | Illumination control method and illumination device |
JP2000276094A (en) * | 1999-03-29 | 2000-10-06 | Fuji Photo Film Co Ltd | Gradation correcting method and picture display system |
US20020052724A1 (en) * | 2000-10-23 | 2002-05-02 | Sheridan Thomas B. | Hybrid vehicle operations simulator |
US6862022B2 (en) * | 2001-07-20 | 2005-03-01 | Hewlett-Packard Development Company, L.P. | Method and system for automatically selecting a vertical refresh rate for a video display monitor |
JP3783645B2 (en) * | 2002-04-05 | 2006-06-07 | 株式会社日立製作所 | Contrast adjustment method, contrast adjustment circuit, and video display device using the same |
TWI243616B (en) * | 2003-12-24 | 2005-11-11 | Tatung Co Ltd | Method for adjusting brightness of display |
TW200612364A (en) * | 2004-10-08 | 2006-04-16 | Tatung Co Ltd | Method and device adjusting luminance of display device |
JP4438696B2 (en) * | 2005-06-15 | 2010-03-24 | セイコーエプソン株式会社 | Image display apparatus and method |
KR100774203B1 (en) * | 2006-06-27 | 2007-11-08 | 엘지전자 주식회사 | Control method for display character of television receiver and the television receiver |
US8706271B2 (en) * | 2010-02-18 | 2014-04-22 | Redwood Systems, Inc. | Integration of computing device and lighting system |
US8981913B2 (en) * | 2010-02-18 | 2015-03-17 | Redwood Systems, Inc. | Commissioning lighting systems |
US9572228B2 (en) | 2010-02-18 | 2017-02-14 | Redwood Systems, Inc. | Commissioning lighting systems |
GB2558000B (en) * | 2016-12-21 | 2020-06-10 | Apical Ltd | Display control |
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- 1999-09-10 WO PCT/US1999/020729 patent/WO2000016359A2/en not_active Application Discontinuation
- 1999-09-10 JP JP2000570803A patent/JP2002525898A/en active Pending
- 1999-09-10 AU AU61404/99A patent/AU6140499A/en not_active Abandoned
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Also Published As
Publication number | Publication date |
---|---|
JP2002525898A (en) | 2002-08-13 |
EP1119982A2 (en) | 2001-08-01 |
US6327708B1 (en) | 2001-12-04 |
EP1119982A4 (en) | 2001-12-05 |
WO2000016359A3 (en) | 2000-07-27 |
AU6140499A (en) | 2000-04-03 |
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